You can also attach it with USB on your other Macs. If you have a G-DRIVE w/ TB3 as you mentioned then it has a single USB 3.1 type C on the back and we included a cable that goes from C to A so it can work in older machines.

There is possibly an issue with the new Mac if both TB3 and USB 3 aren’t working. You can contact Apple to see if they can assist with a diagnostic test. You can also attempt your own fixes by resetting the SMC and NVRAM. Resetting the SMC

Curious, I have the same issue. TB1 to the TB on the iMac is not functioning… and no USB on the drive. I know its the iMac Thunderbolt adapter that is the issue, but can you add an adapter on the TB1 to TB on the iMac to connect via USB instead? Any other options to connect to the IMac?